High-power liquid fuel composition for spark-ignition engines

ABSTRACT

A high-power liquid fuel composition for spark-ignition engines is provided. The fuel composition has a RON greater than or equal to 95 and a MON greater than or equal to 85, the RON and MON values being measured according to the ASTM D 2699-86 standard or D 2700-86 standard, and includes at least one C4-C5 unsaturated alcohol. The disclosure also relates to the use of a C4-C5 unsaturated alcohol, preferably 3-methyl-2-butene-1-ol or 3-methyl-3-butene-1-ol, in a petrol fuel composition, for improving the power of a naturally-aspirated or turbocharged spark-ignition engine, during the combustion. The disclosure also relates to a process for preparing such a fuel composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase Entry of International Application Serial No. PCT/EP2013/053792, filed on Feb. 26, 2013, which claims priority to French Patent Application Serial No. 1251766, filed on Feb. 27, 2012, both of which are incorporated by reference herein.

BACKGROUND AND SUMMARY

The present invention relates to liquid fuel compositions for spark-ignition engines of the petrol type, naturally-aspirated or turbocharged, and more particularly, high-power petrol fuel compositions and their use.

The petrol-type fuels that can be used in naturally-aspirated or turbocharged spark-ignition engines, in particular those of motor vehicles, have octane numbers that are sufficiently high to avoid the knock phenomenon. Typically, the petrol fuels marketed in Europe, complying with the EN 228 standard, have a Motor Octane Number (MON) above 85 and a Research Octane Number (RON) of 95 as a minimum. These fuels are suitable for the great majority of automotive engines.

For high-power engines and, in particular, for automotive competition engines, the principal qualities desired for fuels supplying a competition engine are:

-   -   a high net heating value (NHV), whether by volume or mass. The         NHV represents the quantity of energy comprised in a given         volume or mass of fuel. The higher this energy value, the more         heat it will be possible to extract from the fuel. This thermal         energy can subsequently be converted by the engine into         mechanical energy in order to extract more power therefrom. For         certain applications, the increase in the mass or volume NHV         will make it possible to increase the range while racing and         therefore to reduce the frequency of refueling;     -   a high speed of combustion. The speed of combustion represents         the speed at which the flame front propagates in the combustion         chamber. The speed of combustion makes it possible to reach the         pressure peak in the chamber during the process of a combustion         cycle more quickly, impacting on the quality of the engine         output. An increase in the speed of combustion makes it possible         to reduce the duration of a combustion phase, which is a         parameter of prime importance in achieving power in engines         having a high speed of rotation.     -   a high resistance to engine knock and pre-ignition with high         “research” (RON) and “motor” (MON) octane numbers. If the octane         numbers are insufficient with respect to the compression ratio         applied in the engine, the knock phenomenon or fuel pre-ignition         can occur, which can significantly damage the engine and         dramatically reduce its performance.     -   An optimized oxygen content. As the oxygen-containing compounds         introduced into the formulations of the petrols have a latent         heat of vaporization greater than those of the hydrocarbon         molecules, they will have the great advantage during the         injection of the fuel of increased cooling of the air stream,         thus increasing the intake of air. It is necessary however to         know how to manage the oxygen contributed by the fuel in order         not to too much reduce the air/fuel ratio if the fuel is too         rich in oxygen.

In order to vary the mass or volume NHV, several families of molecules have historically been used: nitroparaffins, in particular nitromethane which has a mass NHV of 10512 kJ/kg, have been used in competition fuel compositions. But, nitromethane, like nitroparaffins, is now prohibited in the majority of motor sports competition regulations. Other compounds have also been researched and used in competition fuels. In order to increase the NHV, it is possible to use aromatic structures (toluene, xylene) or also compounds of cyclodiolefin type (for example cyclopentadiene) or diolefins (for example butadiene or isoprene). It is also known that naphthenes, for example cyclopentane, olefins, for example diisobutene, and certain aromatics, in particular ethylbenzene, burn more rapidly than other fuel components on average (source J. C. Guibet, Editions Technip, 1997 edition, Chapter 7, Les carburants pour la competition automobile, page 732-739).

By way of example, document U.S. Pat. No. 4,812,146 describes lead-free petrol fuel compositions for competition engines comprising at least four components selected from butane, isopentane, toluene, MTBE (methyl tert-butyl ether) and an alkylate. Document WO 2010/014501 describes lead-free petrol fuel compositions comprising at least 45% by volume of branched paraffins, at most 34% by volume of one or more mono- and dialkylated benzenes, from 5 to 6% by volume of at least one linear paraffin having 3 to 5 carbon atoms (notation C3-C5), one or more alkanols having from 2 to 4 carbon atoms (notation C2-C4), in sufficient quantity to increase the octane number i.e. (RON+MON)/2 to at least 93. These are high-torque and maximum-power compositions.

The purpose of the present invention is to improve the performance of petrol fuel compositions, in particular competition fuel compositions. The objective is to increase the power of a naturally-aspirated or turbocharged spark-ignition engine, during combustion of the petrol fuel composition in said engine. This purpose is achieved by the use of at least one C4-C5 unsaturated alcohol in a petrol fuel composition, for improving the power of a naturally-aspirated or turbocharged spark-ignition engine during combustion.

The subject of the present invention is based on the applicant's observation that the addition of a C4-C5 unsaturated alcohol in a fuel composition has an effect known as a “power booster” on a spark-ignition engine, naturally-aspirated or turbocharged, during combustion of said fuel. This “booster” effect is even more marked for a turbocharged spark-ignition engine. By “power booster” is meant an increase in the power released during combustion of said fuel in an engine due to the addition of said alcohol in the fuel, in other words, the obtaining of a power improvement in engine speed by the addition of said alcohol to the fuel.

In particular, the invention relates to the use of at least one C4-C5 unsaturated alcohol in a petrol fuel composition, for improving the power by at least 2 hp (horsepower) for engine speeds ranging from 3000 to 8250 rpm, 2 hp corresponding to approximately 1472 Watt. According to a particular embodiment, the petrol fuel composition is a competition fuel composition. The present invention relates to liquid fuel compositions of petrol type the RON of which is preferably greater than or equal to 95 and the MON greater than or equal to 85, the RON and MON values being measured according to the ASTM D 2699-86 standard or D 2700-86 standard and comprising at least a C4-C5 unsaturated alcohol i.e. having 4 to 5 carbon atoms.

The invention proposes an alternative to the existing high-power petrol fuel compositions and, in particular, for automotive competition petrol fuels (for rallies, circuit racing) the characteristics of which currently in force are given in Article 9.1 of the Fédération Internationale de l'Automobile (FIA) Regulations, Annexe J—Art 252, published on Nov. 11, 2010, and are set out below:

-   -   For petrols containing lead i.e. a content less than or equal to         0.4 g/L:         -   RON comprised between 97 and 100         -   MON comprised between 86 and 92     -   For lead-free petrols:         -   RON comprised between 95 and 102         -   MON comprised between 85 and 90             The MON and RON are measured according to the ASTM D 2699-86             standard or D 2700-86 standard.     -   Density measured according to the ASTM D 4052 standard comprised         between 720 and 785 kg/m³     -   Maximum oxygen content less than 2.8% by mass or less than 3.7%         m if the lead content is less than 0.013 g/L,     -   Maximum nitrogen content less than 0.5% by mass, measured         according to ASTM D 3228,     -   Benzene content less than 5% by volume, measured according to         the ASTM D 3606 standard,

The present invention also relates to a petrol fuel composition having the characteristics stated above and comprising at least one C4-C5 unsaturated alcohol. The C4-C5 unsaturated alcohol is preferably selected from 3-methyl-2-butene-1-ol, also known as Prenol, and 3-methyl-3-butene-1-ol, also known as isoPrenol, and their mixture. A preferred composition comprises a single C4-C5 unsaturated alcohol, preferably Prenol or isoPrenol.

The fuel composition preferably comprises from 3 to 22% by volume, advantageously from 5 to 15% by volume, more preferably from 5 to 10% by volume of at least one C4-C5 unsaturated alcohol. The composition preferably comprises 3-methyl-2-butene-1-ol and/or 3-methyl-3-butene-1-ol, alone or in mixture with at least one other C4-C5 unsaturated alcohol. A preferred fuel composition comprises from 3 to 22% by volume, preferably from 5 to 15% by volume, more preferably from 5 to 10% by volume of a single C4-C5 unsaturated alcohol, advantageously, 3-methyl-2-butene-1-ol or 3-methyl-3-butene-1-ol.

DETAILED DESCRIPTION

According to a first particular embodiment, the fuel composition comprises:

-   -   from 20 to 35% by volume of aromatic hydrocarbons, preferably         selected from the alkylbenzenes,     -   from 22 to 35% by volume of C6-C9 isoparaffins,     -   from 5 to 15% by volume of C4-C5 isoparaffins,     -   from 14 to 50% by volume of one or more C4-C5 diolefins         preferably having two conjugated ethylene bonds;     -   from 3 to 22% by volume, preferably from 5 to 15% by volume, of         at least one C4-C5 unsaturated alcohol.     -   from 0 to 6% by volume of one or more C1-C4 paraffinic or         isoparaffinic alcohols, such as methanol, ethanol, isopropanol         and isobutanol;     -   from 0 to 5% by volume of at least one alkyl ether, preferably         selected from MTBE (methyl tert-butyl ether), ETBE (ethyl         tert-butyl ether) and their mixture,     -   from 0 to 6% by volume of one or more C8 isoolefins, such as         diisobutylene.

According to a second particular embodiment, the fuel composition comprises:

-   -   from 20 to 35% by volume of aromatic hydrocarbons, preferably         selected from the alkylbenzenes,     -   from 22 to 35% by volume of isooctane,     -   from 5 to 15% by volume of isopentane,     -   from 14 to 50% by volume of isoprene,     -   from 3 to 22% by volume, preferably from 5 to 10% by volume, of         at least one C4-C5 unsaturated alcohol,     -   from 3 to 6% by volume of one or more C1-C4 paraffinic or         isoparaffinic alcohols and,     -   from 3 to 6% by volume of one or more C8 isoolefins, such as         diisobutylene.

According to a third particular embodiment, the fuel composition comprises:

-   -   from 28 to 34% by volume of aromatic hydrocarbons, preferably         selected from the alkylbenzenes, advantageously toluene;     -   from 22 to 28% by volume of isooctane,     -   from 5 to 10% by volume of isopentane,     -   from 14 to 50% by volume of isoprene,     -   from 3 to 22% by volume, preferably from 5 to 10% by volume, of         at least one C4-C5 unsaturated alcohol,     -   from 3 to 7% of one or more C1-C4 paraffinic or isoparaffinic         alcohols and     -   from 3 to 8% of one or more C8 isoolefins, such as         diisobutylene.

In the first, second and third particular embodiments described above, the C4-C5 unsaturated alcohol is preferably selected from 3-methyl-2-butene-1-ol, 3-methyl-3-butene-1-ol and their mixture. Moreover, the fuel composition can advantageously comprise a single C4-C5 unsaturated alcohol, preferably 3-methyl-2-butene-1-ol or 3-methyl-3-butene-1-ol. In particular, the composition can comprise from 5 to 10% by volume of a single C4-C5 unsaturated alcohol constituted by 3-methyl-2-butene-1-ol.

For each of the first, second and third particular embodiments, the sum of the percentages by volume of the constituents of the composition can advantageously be equal to 100%.

Apart from the hydrocarbon-containing and oxygen-containing compounds listed above, the petrol fuel compositions according to the invention can comprise one or more additives. In particular, the petrol fuel composition can comprise at least one detergent additive, known per se, ensuring the cleanliness of the inlet system. Other additives can also be incorporated in the fuel compositions according to the invention, such as anti valve-seat recession additives and antioxidants.

In order to ensure maximum safety during refueling, it is also preferable for the electrical conductivity of the fuel to be greater than 200 pS/m. For this purpose, at least one additive lowering the electrical conductivity can be added.

The subject of the present invention also relates to a process for the preparation of a petrol fuel composition as previously defined. The process can consist of mixing in chosen quantities the pure chemical compounds constituting the fuel composition, such as for example mixing toluene, isooctane, isopentane, isoprene and 3-methyl-2-butene-1-ol.

It is also possible to mix fuel bases and/or cuts, in particular hydrocarbon bases and/or cuts, originating from the refining of petroleum products. The bases and/or cuts originating from refineries are well known to a person skilled in the art of refining petroleum products. Thus, in order to obtain a mixture of aromatic hydrocarbons of the alkylbenzene type, of isooctane and of isopentane, it is possible to use reformate, alkylate, isomerate and FCC (Fluid Catalytic Cracking) bases which are hydrocarbon-containing bases easily available from refining.

It is also possible to mix fuel bases and/or cuts originating from the refining of petroleum products and pure chemical compounds. The pure chemical compounds can originate from other sources, in particular for ethers, saturated or unsaturated alcohols, olefins and diolefins.

The reformate-type bases are constituted essentially by alkylaromatics (or simply aromatics). The reformate bases in general originate from the reforming of direct-distillation petrols and of isopentane. The reformates are generally constituted by a hydrocarbon-containing cut containing at least 70%, preferably at least 85% by volume of aromatics, comprising toluene (generally from 35 to 75%, preferably 45 to 70% by volume), C8 alkylaromatics (generally from 15 to 50% by weight of ethylbenzene, and ortho-, meta-, para-xylene) and C9 alkylaromatics (generally from 5 to 25% by weight of propylbenzene, methylethylbenzenes and trimethylbenzenes).

As the absolute contents and relative proportions of the different components can vary with the cut points, the nature of the feedstock sent for reforming, the type of catalyst used and the operating conditions of the reforming. Preferably, the reformate-type bases utilized within the framework of the present invention contain less than 1% by volume of benzene. Apart from the aromatic compounds, the reformate bases can in particular contain paraffins, iso- and n-paraffins, generally present in quantities less than or equal to 5% by volume.

The alkylate-type bases are constituted essentially by isoparaffins comprising from 6 to 9 carbon atoms and preferably of at least 90% by volume of isoparaffins comprising from 6 to 9 carbon atoms. The alkylates generally comprise at least 95%, preferably at least 98.5% by volume of isoparaffins including at least 65%, preferably at least 70%, and advantageously at least 80% by volume of C8 isoparaffins. The alkylate bases can contain at least 45%, preferably at least 48% by volume of isooctane, and advantageously at least 30%, preferably at least 34% by volume of other C8 isoparaffins.

These alkylate bases can originate from different crude oil treatment processes generally present in refineries. The alkylate bases conventionally originate from the process of alkylation of isobutane by light olefins, for example butene-1, which will result in isooctane. The preferred alkylate bases contain a majority of isooctane.

The isomerate-type bases are light bases belonging to the family of the paraffinic hydrocarbons. They are constituted essentially by C4 and/or C5 isoparaffins and comprise, preferably at least 80% by volume, advantageously at least 90% by volume, of C4 or C5 isoparaffins. They preferably comprise at least 90% by volume of isopentane and advantageously at least 95% by volume of isopentane: this is then known as an isopentane cut. The isomerate bases generally do not contain more than 1% by volume of olefins. These light paraffinic bases can, for example, originate from the lightest fractions of distillate produced by atmospheric distillation of crude oil and/or originating from alkane isomerization units.

The bases or FCC petrol cuts that have undergone fluid catalytic cracking are rich in aromatics and olefins. The olefins can originate from refineries and/or from renewable materials. By way of example, isoprene can be mentioned, which can originate from naphtha cracking, but also from plants or animals which synthesize it, although in very small quantities.

The C1-C4 alcohols may or may not originate from renewable resources of vegetable origin (for example ethanol originating from beet, maize, sugar cane, etc.) but also from algae or from the fermentation of micro-organisms. Although they can originate from oil refining, unsaturated alcohols and diolefins require a significant number of separation and purification steps going beyond the usual refining operations. Rather, these compounds are incorporated in the pure chemical form.

Nor will the scope of the invention be exceeded by adding other bases originating from conventional refining operations (for example crude oil distillation, catalytic cracking, hydrocracking, reforming, isomerization, alkylation processes etc.) and/or synthetic hydrocarbons such as in particular those obtained by oligomerization of olefins, by Fisher-Tropsch synthesis, by processes of the BTL (biomass to liquid), CTL (coal to liquid) and/or GTL (gas to liquid) type, from materials of natural and/or synthetic origin, of animal and/or vegetable and/or fossil origin. Each base or cut going into the fuel composition according to the invention may have undergone, wholly or partially, a desulphurization and/or denitrogenization and, optionally, dearomatization treatment at any stage of its preparation. For example, bases can be used that have been hydrotreated under more or less severe conditions (comprising hydrodesulphuration and/or saturation of the aromatic and olefinic compounds and/or hydrodenitrogenization). Within the meaning of the present invention, a hydrocarbon base or cut “constituted essentially by the compounds . . . ” means that said compounds represent at least 70% of the volume of said base.

The fuel compositions according to the invention advantageously have a sulphur content measured according to the ASTM D1266 standard or ASTM D2622 standard that is less than or equal to 100 ppm by mass, preferably less than or equal to 50 ppm by mass, and even more advantageously less than or equal to 10 ppm by mass. The fuel compositions according to the invention have a lead content generally less than or equal to 0.5 g/L (added for example in the form of tetraethyl lead) and preferably are lead-free i.e. do not contain any lead or additives with added lead.

A subject of the invention is also the use of a fuel composition as previously defined as a fuel for a high-power spark-ignition engine, preferably for a naturally-aspirated or turbocharged competition engine for circuit racing and rallies. The present invention also relates to the use of at least one C4-C5 unsaturated alcohol in a petrol fuel, for improving the power of the spark-ignition, naturally-aspirated or turbocharged engine during combustion, by at least a 2 hp power difference, advantageously at least 3 hp, according to the engine speed in question, for engine speeds ranging from 3000 to 8250 rpm, by comparison with an oxygenated competition petrol with a RON of 101.5 and a MON of 89.5. According to a particular preferred embodiment, the C4-C5 unsaturated alcohol(s) is/are incorporated into a petrol fuel utilized in a turbocharged engine for improving its power.

Preferably 3-methyl-2-butene-1-ol and/or 3-methyl-3-butene-1-ol are used, the presence of 3-methyl-2-butene-1-ol being particularly preferred. The volumetric concentration of C4-C5 unsaturated alcohol in the petrol fuel is preferably comprised between 3 and 22%, more preferably between 5 and 15%, even more preferably from 5 to 10% by volume. Preferably a single C4-C5 unsaturated alcohol is used, advantageously 3-methyl-2-butene-1-ol. The volumetric concentration of 3-methyl-2-butene-1-ol in the petrol fuel is preferably comprised between 3 and 22%, more preferably between 5 and 15%, even more preferably from 5 to 10% by volume.

EXAMPLE Preparation of a Competition Fuel Composition

A competition fuel composition is prepared by mixing pure chemical compounds listed in Table 1 below at ambient temperature.

TABLE 1 Component (vol %) Fuel C Xylene 31 Isooctane 25 Isopentane 7 3-methyl-2-butene-1-ol 8 Isoprene 18 Ethanol 5 Diisobutylene 6 Total 100

Power Test

The fuel C of the previous example as well as a competition fuel marketed by the company TOTAL Additifs & Carburants spéciaux (TACS) under the name Elf Turbo Evo underwent a power test in a 1.6 L direct-injection turbocharged petrol engine. The characteristics of the fuels C and Elf Turbo Evo are summarized in Tables 2 and 3 below.

TABLE 2 Elf Turbo FIA/Annexe J Evo Fuel C Regulation Octane numbers RON 101.7 101.5  95 to 102 MON 88.6 87.8 85 to 90 Density kg/L at 15° C. 0.770 0.765 0.720 to 0.785 Oxygen Content % mass 3.5 3.4  3.7 max Lead content g/L <0.013 <0.013 0.013 max Sulphur Content mg/kg 6 2   10 max

TABLE 3 Results of analysis by high-resolution gas chromatography for determining the percent by volume of the paraffinic, olefinic, naphthenic and aromatic compounds according to the ASTM 6730 standard test, said analysis being known as PONA analysis, and results of the analysis for determining the percent by volume of the saturated or unsaturated oxygen-containing compounds according to the D4815 standard. Elf Turbo Evo Fuel C Volume % Volume % ASTM 6730 Paraffins 36 35 Olefins 12 22 Naphthenes 0 0 Aromatic 42 30 ASTM D4815 Saturated oxygens 10 5 Unsaturated oxygens 0 8

The details of the power test are given below. This is a direct-injection 1598 cm³ 16-valve in-line 4-cylinder engine with a twin-scroll turbocharger. The maximum engine speed is limited to 9000 rpm. The power test practiced consists of establishing power curves for engine speeds ranging from 3000 to 8250 rpm in 500 rpm steps and making a plot at 8250 rpm.

The results are given in Table 4 below. The results shown represent a power difference in hp measured by comparison with an oxygenated competition petrol of RON 101.5 and of MON 89.5.

TABLE 4 Engine Speed (rpm) Elf Turbo Evo Fuel C 3000 9 11 3500 7 12 4000 8 13 4500 9 13 5000 8 13 5500 6 11 6000 3 6 6500 0 3 7000 2 4 7500 3 5 8000 3 4 8250 3 4

An additional power gain can be observed with the fuel C by comparison with the Elf Turbo Evo fuel of a minimum of 2 hp depending on the engine speed in question. The power gain can reach 6 hp at 4000 rpm. Compared to the competition petrol that allowed the baseline to be established, the fuel C allows a power gain capable of reaching 13 hp over the engine speed range from 4000 to 5500 rpm. 

1. A method for improving the power of a naturally-aspirated or turbocharged spark-ignition engine during combustion of a petrol fuel composition, the method comprising adding at least one C4-C5 unsaturated alcohol in the petrol fuel composition.
 2. The method according to claim 1, wherein the power improvement is at least 2 hp for engine speeds ranging from 3000 to 8250 rpm.
 3. The method according to claim 1, wherein the petrol fuel composition is a competition fuel composition.
 4. The method according to claim 1, comprising improving the power of a turbocharged engine.
 5. The method according to claim 1, wherein the petrol fuel composition has a RON greater than or equal to 95 and a MON greater than or equal to 85, the RON and MON values being measured according to the ASTM D 2699-86 standard or D 2700-86 standard.
 6. The method according to claim 1, wherein the C4-C5 unsaturated alcohol is selected from 3-methyl-2-butene-1-ol, 3-methyl-3-butene-1-ol and their mixture.
 7. The method according to claim 1 wherein the composition comprises a single C4-C5 unsaturated alcohol.
 8. The method according to claim 1, wherein the composition has: a density measured according to the ASTM D 4052 standard comprised between 720 and 785 kg/m³; a maximum oxygen content less than 2.8% by mass or less than 3.7% by mass if the lead content is less than 0.013 g/L; a maximum nitrogen content less than 0.5% by mass; a benzene content less than 5% by volume, measured according to the ASTM D 3606 standard; a RON comprised between 97 and 100 and a MON comprised between 86 and 92, measured according to the ASTM D 2699-86 standard or D 2700-86 standard, when the lead content of the fuel is non-zero and less than or equal to 0.4 g/L; and a RON comprised between 95 and 102 and a MON comprised between 85 and 90, measured according to the ASTM D 2699-86 standard or D 2700-86 standard, when the lead content of the fuel is zero or less than 0.4 g/L.
 9. The method according to claim 1, wherein the composition comprises moreover one or more additives.
 10. The method according to claim 1 wherein the composition comprises: from 20 to 35% by volume of aromatic hydrocarbons; from 22 to 35% by volume of C6-C9 isoparaffins; from 5 to 15% by volume of C4-C5 isoparaffins; from 14 to 50% by volume of one or more C4-C5 diolefins; from 3 to 22% by volume, from 0 to 6% by volume of one or more C1-C4 paraffinic or isoparaffinic alcohols; from 0 to 5% by volume of at least one alkyl ether; and from 0 to 6% by volume of one or more C8 isoolefins.
 11. The method according to claim 1, wherein the composition comprises: from 20 to 35% by volume of aromatic hydrocarbons; from 22 to 35% by volume of isooctane; from 5 to 15% by volume of isopentane; from 14 to 50% by volume of isoprene; from 3 to 22% by volume of at least one C4-C5 unsaturated alcohol; from 3 to 6% by volume of one or more C1-C4 paraffinic or isoparaffinic alcohols; and from 3 to 6% by volume of one or more C8 isoolefins.
 12. The method according to claim 11, wherein the sum of the percentages by volume of the constituents of the composition is equal to 100%.
 13. The method according to claim 1, wherein the composition comprises from 5 to 15% by volume of at least one C4-C5 unsaturated alcohol.
 14. The method according to claim 7, wherein the composition comprises a single C4-C5 unsaturated alcohol chosen from 3-methyl-2-butene-1-ol or 3-methyl-3-butene-1-ol.
 15. The method according to claim 10, wherein aromatic hydrocarbons are selected from the alkylbenzenes.
 16. The method according to claim 10, wherein the C4-C5 diolefins have two conjugated ethylene bonds.
 17. The method according to claim 13, wherein the composition comprises from 5 to 15% by volume of 3-methyl-2-butene-1-ol. 